test: add X-Request-ID middleware coverage

[Shaivpidadi]

Summary

• add tests/test_request_id.py to verify /api/v1/health returns an X-Request-ID header
• assert the header value matches a UUIDv4
• assert a fresh request ID is generated on each request

Validation

• ./venv/bin/python -m pytest tests/test_request_id.py -v exercises both new assertions, but the command exits non-zero because the repo enforces a global --cov-fail-under=60 threshold even for narrow test selection
• ./venv/bin/python -m pytest tests/ -v